In the prior art in certain instances, it has been possible to use the technique known as "pulse stuffing" to allow either a gap or a meaningless signal to be "stuffed" into a data train at periodic intervals in order to increase the apparent data rate of the signal so that it may be carried on higher data rate digital transmission lines without effectively increasing the data. This involes inserting the meaningless signal at the transmit end of a transmission line and providing a stuff control code which indicates where that meaningless signal is on the data line relative to real data on the line. For example, the stuff control code might provide pulses, or digital ones, when the data is on the line and no pulses, or digital zeros, when the stuffed information is on the line. This code permits removal of the stuffed information at the other end of the data line by deleting from the received signal the meaningless portion as indicated by the stuff control code which is transmitted separately from the data.
The prior art has used this technique for multiplexing a plurality of digital signals which are not synchronous into a higher speed digital signal for transmission over a single transmission facility.